ngradvert −− compute vertical particle velocity, horizontal volume and mass divergence, vertical wind and vertical mass flux, and hydrometeor terminal velocity for Candis radar data file
ngradvert
-[t|b|c]
Ngradvert expects a three−dimensional, synthesized Candis radar data file produced by ngradcart with the -o option on the standard input. This file is transferred to the standard output with the addition of certain fields. The added fields are the vertical particle velocity (wp), the vertical wind (w), the vertical mass flux (mflux), the horizontal volume divergence (div), the horizontal mass divergence (dflux), the column divergence correction in dflux (dcorr), the particle terminal velocity (wt), and the x and y wind components (u and v). The column divergence correction is the vertical mean of the uncorrected dflux. Various ambient profiles are added as well. The above fields are added to the variable slice section, whereas the ambient density, pressure, and scale height profiles are added to the static slice. Though normally only one variable slice occurs per file, ngradvert will treat an arbitrary number.
The vertical wind is calculated by integrating the mass continuity equation down from cloud top (with the -t flag) or from the bottom up (with the -b flag) in a calculation which is mostly 2nd order accurate (Raymond, Lopez, and Lopez, 1998: Quart. J. Roy. Meteor. Soc., 124, 2005-2034.). The vertical wind is assumed to be zero at both the cloud top and the surface. No column divergence correction is done. If the -c flag is used, downward integration is performed as with -t, but a column divergence correction is done. Ngradvert determines automatically whether an x-y grid or a lat-lon grid has been produced by ngradcart and adjusts the divergence calculation accordingly.
See the source code for the particle terminal velocity calculation. The particle vertical velocity is computed as the sum of the vertical wind and the particle terminal velocity.
The horizontal wind components are computed according to the equations u = ux0 + gx*wp and v = uy0 + gy*wp, where ux0, uy0, gx, and gy are fields generated by radcart5 and wp is the particle vertical velocity.
Units of velocity are m/s, while distance is measured in km. Density is measured in kg/m^3, while pressure is measured in hPa.
Ngradvert doesn’t do extensive checking on the size and dimensions of input fields. If these take on unexpected values, trouble could result.
Bugs occasionally act like hydrometeors.